DRIVE UNIT FOR BOATS

Abstract: Drive unit for boats, comprising an internal combustion engine driving an outboard drive, e.g. a sailboat drive. Insulating elements (24, 26, 27) are disposed between the flywheel casing (11) of the engine and the drive housing (9) in order to electrically insulate them from each other. An electrically insulating coupling (30) connects the engine flywheel (21) to the input shaft (29) of the drive.

Description: Drive unit for boats The present invention relates to a drive unit for boats, comprising an internal combustion engine with a flywheel fixed on a crank shaft and surrounded by a flywheel casing, and a propeller drive with a housing connected to said flywheel casing and an input shaft driven by said crank shaft. In drive units of this type, for example outboard drive units, it is common to make parts of the drive unit, for example the rig, the propellers, the lower transmission housing of alumi- num. Since these components are submerged in the water, it is important to see to it that measures are taken to prevent i.a. galvanic corrosion from shortening the useful life, should the parts be electrically connected to another submerged component of a metal which is more electro-positive, for example a keel of iron with stainless steel bolts which are grounded together with the engine block in a single-pole electric system. The parts of the drive unit submerged under water can be protected by known methods, i.e. by mounting a sacrificial anode on the drive, or by painting with protective paint, or by a combination of these two measures. Another known method of avoiding galvanic corrosion on the propeller drive, e.g. a sailboat drive unit in a sailboat with an iron keel with stainless steel keel bolts, is to equip the boat with a two-pole electrical system, i.e. a system in which each electrical power consumer, such as the starting motor, the generator, the oil pressure sensor etc, is connected to the battery via a positive and a negative conductor. The advantage of a two-pole electrical system is that the drive unit will be insulated from the rest of the electrical system and no attention must be paid to replacing the sacrificial anode or repainting with protective paint. However, it is important that the boat owner, when installing additional equipment for example, does not modify the engine electrical system so that the engine drive units are grounded. The purpose of the present invention is to provide a drive unit of the type described by way of introduction, which permits connecting the engine block to ground and where the electrical power consumers can thus be coupled to the battery via a single pole electrical system without risk that the submerged components of the drive will be subjected to galvanic corrosion. This is achieved according to the invention in a drive unit in which the drive lacks electrically conducting connection to the engine. In a preferred embodiment of the invention applied to known inboard and outboard drives with a metal transition housing, which has a flange screwed securely to a flange on the flywheel casing of the engine, and in which the input shaft of the drive can be drivingly connected to the flywheel via an elastic coupling, the screws are mounted in bushings of insulating material. Spacer elements of insulating material are arranged between the flanges and between the bolt heads and the flange of the drive housing. The flywheel is joined to the input shaft of the drive via an elastic coupling which has coupling halves which are electrically insulated from each other. The invention will be described in more detail with reference to examples shown in the accompanying drawings, where Fig. 1 shows a schematic sideview of a drive unit according to the invention in a schematically indicated sailboat hull, and Fig. 2 shows a longitudinal section through the encircled area in Fig. 1. The numeral 1 in Fig. 1 indicates a sailboat hull with a keel 2a and a rudder 2b spaced from each other. The keel can be made of iron or lead and have stainless steel keel bolts 3 cast therein, which are screwed fast to the inside of the hull by means of nuts 4. A drive unit consisting of an internal combustion engine 5, preferably a diesel engine, and a propeller drive 6 is bolted securely to an engine bed (not shown). The drive 6 is a so-called S-drive and has a rig leg 7 which extends out through a sealed opening in the bottom of the hull. The drive 6 is suspended in the engine 5 in a known manner by bolting a flange 8 on the upper transmission housing 9 of the drive unit to a flange 10 on the engine flywheel casing 11, as will be described in more detail with reference to Fig. 2. The engine battery 12 has its minus pole connected to keel bolt 3 and the engine block 5. The numeral 20 in Fig. 2 indicates the distal end of the engine crank shaft, to which a fly¬ wheel 21 is bolted and which is surrounded by the flywheel casing 11. The flange 8 on a wall 22 of the upper transmission housing 9 of the drive is made with a number of bores 23 into which bushings 24 of electrically insulating material, e.g. a plastics material, are forced. The flange 20 on the flywheel casing 21 has corresponding threaded bores 25. Washers 26, 27 of insulating material, e.g. a plastics material, are disposed on either side of the respec¬ tive bushing 24, thus completing the electrical insulation from each other of the flywheel casing 11 and the upper transmission housing 9 of the drive, when the components are bolted 28 together. The engine flywheel 21 is joined to an input shaft 29 to the upper transmission housing 9 of the drive, via an elastic coupling, generally designated 30, which comprises a metal ring 31 screwed securely to the flywheel 21, a metal disc 33 non-rotatably connected said input shaft via a splines connection 32, and an intermediate ring 34 of an elastic material, e.g. rubber, which is vulcanized fast to the ring 31 and the disc 33. A groove 35 opening to¬ wards the flange 8 has a guide ring 36 of electrically insulating material, against which a guide surface on a guide shoulder 37 on the drive housing flange 8 abuts. Thus, there is no metallic connection between the ring 31 and the disc 33 nor between the flanges 8 and 10, which means that no galvanic couple can be formed with the rig leg as an anode. The invention has been described above with reference to a propeller drive of outboard type, but of course the invention is not limited to this type of propeller drive but also comprises propeller drives of inboard type, which, although lacking a rig leg of aluminum, can protect a bronze propeller for example against corrosion by insulating the engine and the crank shaft from the shaft housing and the input shaft.

Claims: CLAIMS 1. Drive unit for boats, comprising an internal combustion engine with a flywheel fixed on a crank shaft and surrounded by a flywheel casing, and a propeller drive with a housing connected to said flywheel casing and an input shaft driven by said crank shaft, characterized in that the propeller drive (6) has no electrically conducting connection with the engine (5). 2. Drive unit according to claim 1, characterized in that the drive housing (9) has a flange (8) which is fixed to a flange (10) on the drive wheel casing (11) by means of screws (28) electrically insulated from surrounding metal components by means of bushings (24) and spacer elements (26,27) of insulating material. 3. Drive unit according to claim 2, characterized in that the flange (8) of the drive housing has through bores (23), in which bushings (24) of insulating material for the screws (28) are disposed and that the screws extend through washers (26,27) of insulating material disposed on either side of the bushings. 4. Drive unit according to claim 2 or 3, characterized in that the flange (10) of the flywheel casing has a groove (37) opening towards the drive housing flange (8), in which groove a guide ring (36) of insulating material is disposed, and that the drive housing flange is provided with an axial guide shoulder (37) which has a guide surface facing said guide ring. 5. Drive unit according to one of claims 1-4, characterized in that the input shaft (29) of the drive is driveably connected to the flywheel (21) via an elastic coupling (30) which has coupling components (31,33) electrically insulated from each other. 6. Drive unit according to claim 5, characterized in that the coupling (30) has an annular metal element (31), which is screwed securely to the flywheel (21), and a disc-shaped metal element (33), which is connected to the input shaft (29) by means of a splines connection (32), and that at least one element (34) of an elastic and electrically insulating material is bonded to the two metal elements. 7. Drive unit according to one of claims 1-6, characterized in that the propeller drive is an outboard drive (6) with a rig leg (7), designed to extend through an opening in the bottom of a boat.

Inventors: EKWALL RAGNAR, EKWALL, RAGNAR
Applicants: EKWALL RAGNAR, VOLVO PENTA AB, AB VOLVO PENTA, EKWALL, RAGNAR
Application year: 1994
Main classification: B63H21
IPC codes: B63B59, B63H21